1. Field of the Invention
The present invention relates to a method and apparatus for receiving digital broadcasting data, and more particularly, to a method and apparatus for receiving digital broadcasting data which can be applied uniformly to in-band channels and out-of-band channels by defining a new network service access point (NSAP) format.
2. Description of the Related Art
Digital broadcasting has enabled new application fields through digitalization of broadcasting contents. One of these new application fields is multimedia broadcasting.
Multimedia broadcasting is a new concept of broadcasting service which is differentiated from the conventional audio and video broadcasting using analog, or digital signals, and radios and TVs. While the services of the conventional broadcasting are limited to only simple transmission of voice and images, multimedia broadcasting provides a variety of new services unimagined by the conventional broadcasting, by transmitting digital data through broadcasting channels.
For example, while KBS, a service provider, broadcasts a movie program, Troy, through a transmission line, KBS can make information on the production process and so on of Troy, be displayed to viewers. Then, when broadcasting the program, Troy, KBS transmits three types of data, including video data, audio data, and service data. A terminal receives the three types of data, then decodes the video and audio data by using a decoder, and reproduces the data. The service data is processed by an application program of the terminal or an application program received through a transmission line, and then the processed result is output through display apparatus to a user.
FIGS. 1A and 1B are diagrams showing a service information table (SIT) and a program mapping table (PMT), respectively.
The three types of data transmitted in digital broadcasting are processed in the form of files and data streams. When files are transmitted, all files are divided into packets of a predetermined length. By the nature of broadcasting, packets are repeatedly transmitted and a set of repeated packets is referred to as a carousel. Information on the relation between a packet and a program is transmitted through a separate process from the service provider to a terminal. This information is expressed, for example, as a service information table (SIT), a program mapping table (PMT), and so on. The SIT maps source ID and program number. The source ID is an identifier of a broadcasting provider, and a program number that is an identifier of a broadcast program (FIG. 1A), and the PMT maps a program number and a packet ID (FIG. 1B). The packet ID is an identifier for identifying a packet indicating video data, audio data, and service data included in one program. Based on the packet ID, a terminal obtains a packet corresponding to a program that it requires, from a transmission channel.
Service data is generated by the service provider, and then broadcast to terminals. Service data can be an application program or application data that is referred to by an application program. Hereinafter, in order to distinguish these, the former will be referred to as a service program, and the latter as service reference data. Service data is obtained by a terminal from a transmission channel and is executed by a processor in the terminal. Generally, services programs are written by using Java, HTML, MHEG, etc.
In a service program, there is a locator or a network service access point (NSAP) including information on the location of reference data that is referred to by each service program. The NSAP is defined by ISO/IEC 8348 and is used as an address to identify a network end point in an OSI networking model.
Meanwhile, digital broadcasting is performed through a transmission channel with a limited bandwidth. The transmission channel is divided into an in-band channel (IB) and an out-of-band channel (OOB) according to the size of a bandwidth of the transmission channel.
The in-band channel is a channel through which main data is broadcast according to predetermined broadcasting standards, and generally has a very large bandwidth, and transmits audio data, video data, and service data all together.
In broadcasting through the in-band channel, each broadcasting station is assigned a source ID that is a unique identifier. In the out-of-band channel, broadcasting standards for data transmission are not determined, and the bandwidth is very narrow such that generally audio and video data are not transmitted and only service data is transmitted. In the out-of-band channel, a source ID is not used.
FIG. 1C is a flowchart of the operations performed by a method for receiving data broadcast through an in-band channel.
In operation 110, a receiver obtains audio data, video data, and service data from a transmission line. If the service data is a service program and it is indicated that this service program should refer to another service data, service reference data should also be received.
In operation 120, by analyzing an NSAP existing in the service program obtained in the operation 110, the receiver extracts the source ID of service reference data which the service program desires to refer to.
In operation 130, based on the service information table (SIT), the receiver determines a program number (PN) corresponding to the source ID. The SIT includes a table mapping a source ID and a program number (PN) and is transmitted from the broadcasting provider to receivers in advance according to predetermined protocols.
In operation 140, the receiver determines a packet ID corresponding to the program number based on the program mapping table (PMT).
In operation 150, by extracting packets having the packet ID among all packets received by the receiver, based on the packet ID, the receiver selectively receives those packets.
Unlike the process of FIG. 1C, in broadcasting through an out-of-band channel, a source ID is not determined. Accordingly, based on a program number, the receiver extracts service reference data desired by the user from a transmission line. The program number is transmitted in advance by the broadcasting provider to the receiver.
At present, as a digital broadcasting standard, OpenCable™ Application Platform (OCAP) is being prepared, and research activities for this standard currently being performed are to uniformly process service data both in an in-band and an out-of-band channels.
FIG. 2 is a diagram of the structure of an NSAP according to the conventional OCAP.
Referring to FIG. 2, the conventional NSAP is formed with 20 bytes in total. A private data field for a service program is assigned 10 bytes.
Among a variety of information items for a service program included in the private data field, there is a 2-byte source ID. The source ID indicates location information on a network of service reference data which is transmitted. In digital broadcasting, location information of service reference data on a network is identified by using an NSAP and based on this location information, the service reference data is obtained from a transmission line. The service reference data is data required for performing a service program broadcast, and is data or a program.
Which information should be recorded in the location information of reference data varies depending on digital broadcasting standards. In the specifications of the OCAP or advanced common application platform (ACAP), a source ID is recorded in this service ID. A source ID is an identifier for identifying a service provider broadcasting reference data. At present, in the OCAP, the source ID is 2 bytes long, and each service provider of an in-band channel has a proper value.
Details of the OCAP are available in OpenCable™ Application Platform Specification as of Mar. 5, 2004, and in the specification, details of the NSAP can be found at OCAP specification 3.2.1 Definitions 18p Locator, 16.2.1.1. OCAP 1.0 Locator, and 16.2.1.5 Locators and content referencing. These contents are merged into the present invention.
However, the OCAP standard described above defines only the in-band channel and does not have any definitions on the out-of-band channel. Accordingly, the conventional NSAP shown in FIG. 2 cannot appropriately express location information of reference data incoming through an out-of-band channel.